Dry planographic plates and methods, production and use

ABSTRACT

A new &#39;&#39;&#39;&#39;dry planographic&#39;&#39;&#39;&#39; plate comprised of a flexible substrate having coated thereon a cured solid but elastic silicone rubber film which will not remove conventional lithographic ink from an ink roller on a printing press, a method of producing this plate and a new &#39;&#39;&#39;&#39;dry planographic&#39;&#39;&#39;&#39; process wherein the new planographic plate of the present invention is not wet with a fountain solution.

United States Patent Gipe 1451 July 18, 1972 541 DRY PLANOGRAPHIC PLATESAND 2,744,878 5/1956 Smith-Johannsen ..161l206 x METHODS, PRODUCTION ANDUSE 2,804,388 8/1957 Marron et a1 ...........96/33 3,163,534 12/1964Adamset ...117/16l X Balnmm- 3,179,534 4/1965 Law ...1 17/161 x 73 i Shp" g Delaware County. 3,241,486 3/1966 Greubel et al. 101/457 X Pa.3,385,727 5/1968 Thomas et a1 ..260/46.5 X [22] Filed: Feb. 19, 1968 [2]1 Appl No; 706,286 FOREIGN PATENTS 0R APPLICATIONS new USA ll mun903,964 8/1962 Great Br1ta1n.......................,.101/457 [63]Continuation-impart of Ser. No. 494,768, Oct. 1 1, PrimaryExaminerRobert F. Burnett 1965 abandoned. Assistant Examiner-George W.Moxon, l1

Attorney-John A. Weygandt and John W. Kone, Jr. I521 US. Cl ..l01/4$0,96/33, 96/363, 96/75, 101/456, 101/460, 101/466, 117/37 R,

1l7/45,117/62.2,1l7/13$.1,117/1612A, 57 mer 161/116,161/207,161/209 511111. c1. .1132 25/20, 841m 1/00, B4111 1/12 A new y p ar n platecompmed a flwble sub 5s Field ofSeorch 101/450, 456, 457, 460-467, strawhaving coated thereon a cured solid but elastic silicone l01/453; 96/31,33, 75, 32, 36.3; 1 l7/135.1, 62.2, rubber film which will not removeconventional lithographic 161 ZA, 37 R, 38, 45; 106/2, 23, 24, 25, 28,29; ink from an ink roller on a printing press, a method of produc-204/17; 161/206, 207, 209, 116; 260/465 ing this plate and a new dryplanographic" process wherein the new planographic plate of the presentinvention is not wet [56] References Cited with a fountain solution.

UNITED STATES PATENTS 9 Claims, 6 Drawing Figures 3,511,178 5/1970Curtin ..101/450 3,209,683 10/1965 Greubel ..l01/457 X /W@0/7e rudderf/exl /e 51/65/74 fa DRY PLANOGRAPHIC PLATES AND METHODS. PRODUCTION ANDUSE RELATIONSHIP TO OTHER APPLICATION The present application is acontinuation-in-part of my copending application entitled Method forPreparing Dry Lithographic Plates," Ser. No. 494,768, filed Oct. ll,1965 and now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to a new formof planography or planographic printing which may be called dryplanography. Planography, as the name implies, is printing from aprinting plate or equivalent surface which is substantially level orplane.

The most important branch of conventional planography is lithography,which is based on the mutual repellency of oil and water. In practice, alithographic plate, which may be made of stone, coated or roughenedmetal, coated paper, or coated plastic film, has afiixed thereto animage that is repellent to water but that readily accepts greasyprinting ink. The methods of producing the images are well known tothose skilled in the art. After the plate has been imaged, an aqueouslithographic solution which usually contains an acid phosphate salt isapplied to the plate. The aqueous lithographic solution may also containglycerine or other humectant and gum arabic. The water repellent imageis not wet by the lithographic solution, but the unimaged backgroundareas are all wet by the solution. Following the wetting of the unimagedareas, a roller covered with greasy lithographic printing ink is rolledacross the surface leaving a film of ink on the image but not on the wetbackground areas. This ink film can then be transferred to anothersurface brought into contact therewith, such as the paper sheet indirect lithography or the offset blanket in offset lithography. Beforeanother print is made from the plate, a fountain roller applies moreaqueous lithographic solution to the plate and an inking roller appliesmore ink to the image. Then another print is made. The process can berepeated for as many prints as are desired.

In the history of commercial offset lithography, the fact that watermust be used to prevent ink from sticking to the background has been oneof the major technical problems which has slowed the growth ofcommercial offset lithography. Special inks had to be developed whichwould not mix with the water. Special rollers had to be developed thatwould continue to carry ink in the presence of water and not strip".Special papers had to be developed in which the adhesives wereinsolubilized so that the water would not penetrate and in turn allowthe printing stresses to pull the paper and/or coatings thereon apart.All these developments either made the plates, inks and rollers morecostly to make or led to compromises which resulted in the loss of otherdesirable characteristics. The present invention is directed to a dryplanographic process which eliminates the use of a water fountain andthe attendant difiiculties arising from the use thereof.

Furthermore, in offset lithography a careful balance must be maintainedbetween the amount of ink fed to the printing plate and the amount ofwater applied to the surface of the plate. Too much water causes weakprints and insufficient water allows the non-image areas to pick up inkand to print. With the new plate and new dry planographic process of thepresent invention, only the ink feed needs to be controlled.

The new planographic plate and new dry planographic method of thepresent invention do not require the use of a fountain solution of anytype. The new planographic plate can be completely dry when mounted onthe printing press and is run without having hydrocarbon fountainsolutions as described by Greubel in U.S. Pat. Nos. 3,209,683; 3,241,486and 3,356,030 or water applied to its surface before or during the run.When imaged with an oleophilic image and rolled over the greasy printingink, the oleophilic image takes up the ink, but the silicone rubberbackground of the plate rejects the ink. Therefore, only the oleophilicimage areas print and the background or non-imaged areas remain clean.In another adaptation, when the plate is imaged with a hydrophilicimage, it can be rolled over with water-base or glycol-base ink whichwill adhere to the hydrophilic image but be rejected by the backgroundareas. Thus, the present invention provides an additional advantage overprior art lithographic plates and processes in that the plate of thepresent invention can be imaged with either a hydrophilic or oleophilicimage which allows the use of wither water-base or oil base inks.

This novel plate also permits much simpler press design than eitheroffset lithography or letterpress. Letterpress requires very precisepositioning of the plate for both inking and impression. Massive, costlypresses are required to achieve the desired precision. Such presseswould not be necessary for the use of the plate of the presentinvention. Furthermore, in offset lithography the water applying systemshave never been satisfactory. Improvements in molleton coveringmaterials and fairly complex metering systems have decreased the problemsomewhat, but the water application systems still need furtherrefinement. Dry planography employing the new plates and method of thepresent invention permits the building of a much simpler press without awater or hydrocarbon application system. Along with this simplificationless precautions need to be taken to prevent the corrosion which iscaused by the acidic fountain solutions used in lithography.

In printing metal foils and plastic films by offset lithography, thewater used to wet the plate is very troublesome as it is not absorbed bythe films being printed as it would when paper is being printed. Thiscauses additional problems in ink emulsification, press balance, andunwanted wetting of the product. Dry planography" is, therefore, moresatisfactory for the printing of materials that do not absorb water.

Another unusual and advantageous application of this novel plate is onletterpress machines where the dry plates may be mounted type high oneither a flat bed or rotary press and clean copy may be produced fromthis planar surface since the ink will only be transferred to the platein the image areas. The non-image areas of the plate will not accept inkbecause there is insufficient adhesion between the ink and platesurface.

Various silicon containing materials have been employed in theproduction of lithographic plates, e.g., soluble silicates, U.S. Pat.No. 3,085,008; colloidal hydrated silica and polymerized silicic acid,U.S. Pat. No. 2,714,066; and ink receptive organosilicones, U.S. Pat.No. 2,804,388. In all of these cases, a conventional aqueous fountainsolution is employed to prevent the ink from sticking to the hydrophilicsurfaces. The Greubel et al patents, U.S. Pat. Nos. 3,209,683; 3,24l,486and 3,356,030, employ thermo-setting alkyl and aryl substitutedpolysiloxanes in the production of a planographic plate which must bewet with a hydrocarbon fountain solution to prevent the ink fromadhering to the silicone surface.

SUMMARY OF THE INVENTION The present invention is directed to a newplanographic plate, a method of producing the new planographic plate anda new dry planographic printing method employing the new plates hereindescribed.

The new planographic plate of the present invention comprises a sheet offlexible substrate sufficiently strong to withstand the stressesnormally employed in a lithographic printing process; said substratehaving coated on at least one surface thereof a layer of silicone rubberthat will not remove conventional lithographic printing ink from aninking roller of a printing press.

The term silicone rubber as employed in the present specification andclaims represents a diorganopolysiloxane composition which upon curingto a solid elastic state provides a surface will not remove conventionallithographic printing ink from an inking roller. Representative siliconerubbers to be employed in the present invention result from the curingof a diorganopolysiloxane selected from the group consisting of a.linear diorganopolysiloxanes having terminal siliconbonded acyloxygroups;

b. linear diorganopolysiloxanes having terminal reactive end-blockinggroups and a metal salt of carboxylic acid; and

c. linear fluid diorganopolysiloxanes having terminal silicon-bondedhydroxy groups, a metal salt of an organic carboxylic acid and a memberof the group consisting of an alkyl silicate or methyl hydrogenpolysiloxanes. The term diorganopolysiloxane as employed hereinrepresents disubstituted polysiloxanes wherein the substituents aremonovalent aliphatic or cyanoalkyl groups having from one to four carbonatoms, inclusive. Representative aliphatic and cyanoalkyl groups includemethyl, ethyl, propyl, butyl, vinyl, allyl, betacyanoethyl,beta-cyanopropyl and halo alkyl groups such as 3,3,3-trifluoropropyl andchloromethyl. Representative metal salts of organic carboxylic acidsinclude tin naphthenate, tin octoate, lead octoate, tin oleate, ironstearate, tin butyrate, dibutyl tin dilaurate, dibutyl tin diacetate,zinc naphthenate, lead 2-ethylhexoate and the like with the tin and zincsalts generally being preferred. The term reactive end groups asemployed in the present invention designates acetoxy, hydroxy and oximegroups.

The diorganopolysiloxane compositions employed to produce the solid butelastic silicone rubber films of the present invention are convenientlyapplied to at least one surface of the flexible substrate in the form ofan aqueous emulsion or aqueous or solvent dispersion. Thediorganopolysiloxane compositions are applied to the substrate by meansof a blade coater, Mayer bar, reverse roll coater, knife or by othercommonly employed coating techniques. The surface to be coated should beclean and preferably dry when the diorganopolysiloxane composition isapplied. The silicone rubber film can be of any desired thickness aslong as the film is coherent, continuous and securely bonded to thesubstrate. It has been found convenient to apply thediorganopolysiloxane composition in an amount sufficient to provide acoating of silicone rubber having a thickness of from 0.02 to 0.2 mils.Films thicker than 0.2 mils can be employed; however, they are generallynot deemed to be necessary.

Following the application of the diorganopolysiloxane composition to thesurface of the substrate, the diorganopolysiloxane composition must beallowed to cure to produce the solid but elastic silicone rubber. Mostof the diorganopolysiloxane compositions of the present invention cureat room temperature. The curing generally takes place within minutes to24 hours. However, the curing time will vary according to thickness ofthe film, humidity and temperature. While most of thediorganopolysiloxanes cure at room temperatures and, therefore, do notrequire additional heating, the coated plate can be heated to decreasethe cure time if desired. When employing a diorganopolysiloxanecomposition comprising a fluid diorganopolysiloxane having terminalsilicon bonded hydroxy groups, a metal salt of a carboxylic acid and amethylhydrogen polysiloxane, heat curing is recommended, temperatures offrom 90 to 500 F are operable and temperatures between 90 and 160 F arepreferred. Curing is obtained by heating the film to be cured for aperiod of from about seconds to about 3 minutes or more.

The flexible substrate employed in the present invention should besufficiently flexible that it can be mounted on a lithographic press andstrong enough that it can withstand the stresses normally produced bythe lithographic process. Representative substrates include coatedpapers, metals or plastics such as polyethylene terephthalate). Whilealuminum appears to be the preferred metal substrate on the basis ofcost, handling properties, and the like, sheets of lithographic zinc,foils of copper, steel and copper surfaces all can be employed as theflexible substrate in the present invention.

Any grade of paper can be employed as the substrate in the presentinvention provided that it has the strength to withstand the stressesnormally employed in the lithographic process. Such papers are wellknown in the art and generally range from 70 to 250 pounds per ream. Thediorganopolysiloxane compositions employed to produce the solid butelastic silicone rubber coating can be applied directly to the surfaceof the paper. However, such application often requires the use ofrelatively large amounts of diorganopolysiloxane compositions and theuse of such large amounts is generally not economically desirable.Therefore, in a convenient procedure, the surface of the paper plate isprecoated prior to the application of the diorganopolysiloxanecomposition. The precoat serves to hold out" the aqueous emulsion ororganic solvent carrier employed in the application of thediorganopolysiloxane composition. Coatings which provide the desiredcarrier "hold out and are useful in the present invention includepolyvinyl alcohol, casein, starch, carboxylated starch, hydroxyethylatedstarch, alpha protein, styrene butadiene based coatings, acryliccopolymer coatings, vinyl acetates, fluorocarbons and the like. Suchcoatings may contain fillers, pigments, antifoam agents, spreadingagents and other additives commonly employed in paper coatingcompositions. A coated paper substrate designed to give 15,000 or morecopies is easily provided by a paper base made from moderately beatenchemical wood pulp fibers and weighing from -90 pounds per ream of 500sheets (25 X 38 inches in size). A specific example of a suitable paperis one weighing 87 pounds per ream made from a furnish containing beatenwood pulp fibers of coniferous and deciduous trees, a small portion ofclay filler, rosin size and alum. The paper is then coated on one orboth sides with about l0 pounds per ream dry weight of clay and caseinin a 5:1 ratio. The sheet is then dried and calendered.

BRIEF DESCRlPTlON OF THE DRAWINGS FIGS. 1, 2, 3, 4, 5(0) and 5(b) areenlarged cross-sections of plates having an ink-repellent siliconerubber background.

DETAILED DESCRIPTION The new planographic plate of the present inventionas depicted by FIG. 1 is comprised of a flexible substrate 5 having atleast one surface thereof continuously coated with a film 6 of solid butelastic ink-repellent silicone rubber. Following the curing of thediorganopolysiloxane to obtain the solid but elastic silicone rubberlayer, the plate is ready to be imaged. A short run imaged plate isproduced by passing the plate through a xerographic electrophotographiccopier. In this process, a powder image previously electrostaticallyformed on a selenium'plated drum is transferred by contact to the plate.The plate and image are then heated to cause the powder particles tofuse to each other and to the surface of the plate. The imaged plateproduced in this manner is mounted on a printing press, inked and usedto produce clean copies having no ink in the background areas. Thismethod of imaging the plate is useful for producing copies of line copyand the like.

A pre-sensitized plate as illustrated by FIG. 2 is prepared by applyingto the cured solid but elastic surface of the silicone rubber film 6 oneof the water soluble photo-responsive diazo compounds employed inconventional diam-sensitized lithographic plates. The dried powderedphoto-responsive diazo compound is rubbed over and onto the surface ofthe silicone rubber to produce a photo-responsive diazo layer 13 whichadheres to the surface of the silicone rubber. The excess diazo notadhering to the surface is removed by light brushing, air knife or thelike. The sensitized plate thus prepared is exposed through a negativetransparency 14 to radiation having a wave length of the propermagnitude to initiate the photo-response of the diazo layer. Generally,actinic radiation will be sufficient to initiate the photo-responsivereaction. However, radiation having a wave length outside of the rangeof actinic radiation may be employed when necessary. During theradiation procedure, those areas of the plate exposed to radiationbecome insoluble and oleophilic forming an image area 15 which adheresto the silicone rubber layer 6. Following the radiation or exposureprocedure, the surface of the plate is washed with water to remove theunexposed water soluble diazo compound leaving bared surfaces [6 of inkrepelling silicone rubber as the background. The washed plate is thendried and mounted on a printing press. The rotating ink rollers of thepress are applied to the surface of the plate inking the oleophilicimage areas but leaving the unimaged silicone rubber background areasclear.

in another embodiment of the present invention is illustrated by FIG. 3,the ink repellent silicone rubber is applied to the surface of aconventional pre-sensitized lithographic plate to provide in thenon-imaged areas a silicone rubber surface which will not remove inkfrom ink rollers and, therefore, does not require wetting with afountain solution. This embodiment results in the fonnation of a longrun pre-sensitized plate that can be imaged by exposure through apositive transparency and can be made as follows. A flexible substratesuch as an aluminum-base diazo-sensitized plate as disclosed in the Caseand Jewett US. Pat. No. 2,714,066 or a paper-base sensitized plate asdisclosed in the Brinnick et al U.S. Pat. No. 2,778,735 is prepared. Thediazo-sensitized plate comprised of a substrate and a diazo coating 21is then coated with a layer 22 of silicone rubber as herein defined. Thesilicone rubber is applied by conventional coating methods, and ifdesired. can be further squeegeed or wiped down with a soft cloth toleave a film which after hardening may be as thin as 0.05 mils or even0.02 mils. A thicker film, for example from 0.05 to 0.02 mils, can beleft if desired. A very thin film may harden sufficiently in about halfan hour, especially if the atmosphere is rather humid. But ordinarily,especially for thicker films, it is preferred to let the film age forabout 24 hours before developing an image formed thereon. A latent imageitself can be formed in the film any time after the film has becomereasonably firm by exposure of the plate through a positive transparency23. This exposure insolubilizes the underlying diazo compound in theexposed areas 24, that is the background or non-image area, but leavesthe diazo compound unchanged and still soluble in the image area 26. Thelatent image so formed can then be developed at once, or if desired thedevelopment can be postponed for 24 hours or longer. Development isreadily accomplished merely by swabbing the surface with a cotton padwet with water containing a small amount of a wetting agent such assodium lauryl sulfonate, alkyl phenyl ethers, polyethylene glycol,trimethyl nonyl ether of propylene glycol, polyalkylene glycol ethersand the like. The swabbing does not affect the background area 24 wherethe exposed diazo compound apparently acts to bond the silicone rubberto the underlying base; but in the imaged areas 26 the silicone rubberand the underlying still soluble diazo compound are removed by theswabbing, laying bare the surface of the original substrate. In thosecases where the silicone rubber layer is unusually thick or has beenaged for a considerable period, the swabbing liquid may be a mixture ofequal parts of trichloroethane (sold as P & J cleaner) and xylene andabout one-fourth part of ethylene glycol. The bared surface of thesubstrate in the image area 26 accepts ink from the rotating inkingrollers and prints it either directly upon paper or upon an offsetblanket which will transfer the print to paper. Normally the substrateimage, when dry, will accept either oil-base ink or aqueousbase ink,depending upon which is applied first. In most cases, the layer ofsilicone rubber will be thin enough that the recesses left by itsremoval in the image area are so shallow that the plate can beconsidered to be a planographic plate. Of course, thicker layers ofsilicone rubber can be used, and in such cases the image areas 26 may betoo deep to be inked by the usual inking roller. Deep image recesses maybe filled with ink-receptive matter to make the image flush with theplate surface. For use when printing with greasy lithographic ink iscontemplated the recess filler used should be oleophilic, e.g., aviscous polyvinyl acetate emulsion, asphaltum, lacquers or the like.When use of aqueous ink is contemplated, the recess filler should behydrophilic, for example, a mixture of zinccarboxymethylcellulose andclay, or the like.

In a still further embodiment of the present invention, as illustratedby FIG. 4, a long lasting plate that can be given a latent image byexposure through a negative transparency is made as follows. A flexiblemetal substrate 30 such as aluminum or zinc is coated with from 1 to 50grams per square meter of diorganopolysiloxane composition to formsilicone layer 3]. lmmediately after applying the diorganopolysiloxanelayer 31 and while the layer is still tacky, a sheet of sofi chemicallyetchable metallic foil 33 is pressed into intimate contact with theliquid layer. Representative chemically etchable metallic foils includezinc, copper and aluminum. The sandwich so formed is allowed to age forfrom 12 to 96 hours to permit the silicone rubber to cure or becomesolid, and to form an adhesive bond with the metallic foil 33.Thereafter, the exposed surface of the foil 33 is cleaned by briefimmersion in a standard etching solution, washed and dried. Next theclean and dry surface is given a photopolymerizable photo-resist layer34 and exposed through a negative transparency 36. The exposure hardensand insolubilizes the photopolymerizable material in the exposed areas38 to form a latent image. Thereafter, the surface is swabbed with aphoto-resist developer which removes all the unexposedphotopolymerizable material in area 40 and leaves the underlying foil 33bare, but does not remove the photopolymerized layer in the image area38. Then the surface is again immersed in the same etching solution inwhich the foil 33 had previously been cleaned and allowed to remainthere until all of the foil 33, except that covered by the photopolymerimage, has been dissolved down to the underlying silicone rubberbackground 31. The plate is then thoroughly washed and dried. Thisplate, after the background had been etched away, has an image area ofmetal, still covered by the photopolymer resist, raised slightly abovethe silicone background, and so is not, strictly speaking, aplanographic plate. However, the plate can be used in the same way, andon the same printing press, as the other plates having silicone rubberbackground areas as described above. in such use the rotating inkingrollers and offset blanket will come in contact with the silicone rubberbackground. The silicone rubber background remains free of ink as in thepreviously discussed cases, and does not print on the offset blanket orpaper.

Another embodiment of the present invention as illustrated by FIG. 5 isprepared as follows: a silicated aluminum plate 50 is sensitized with aconventional diazo compound, exposed and developed by swabbing with anaqueous emulsion of lacquer which removes unreacted diazo and leaves alayer of lacquer 51 on the exposed image areas 52. After washing, theentire surface of the plate is again swabbed with aqueous solution of aphoto-responsive diazo compound such as the formaldehyde condensate of aparadiazodiphenyl amine salt or the like to form the layer 53. The plateis then allowed to dry, and thereafter coated with a layer of siliconerubber 54. The silicone layer is cured and the entire plate exposed toradiation of sufficient wave length to initiate the photo-responsivereaction of the diazo compound. By this treatment the diazo compound isinsolubilized and its adherence to the silicone rubber layer isimproved, and likewise the silicone rubber layer itself is furthercured. Next, the plate is swabbed vigorously with a mixture of equalparts of l, l ,l-trichloroethane and xylene and one-fourth part ofethylene glycol which penetrates through the silicone layer 54 andloosens the lacquer layer 51 covering the image area 52. The lacquer andoverlying silicone rubber come away from the image leaving the imagedarea 52 slightly recessed. The plate thus prepared can be used in thiscondition or the recessed areas can be filled with oleophilic materialsuch as viscous polyvinyl acetate emulsion. In the latter case theresulting plate has a level surface, with image areas of oleophilicpolyvinyl acetate and ink-repellent background areas of a siliconerubber.

Other plates can be made by coating a metal or paper plate with a layerof silicone rubber, curing the silicone rubber at room temperature forseveral hours, and then using an engravers tool to cut a pattern throughthe silicone to the underlying base. The pattern is then ink-receptive,but the silicone layer is not. This plate thus prepared can then beemployed on EXAMPLE 1 A paper is prepared from paper stock which iscomposed of about equal amounts of long fibers and short fibers andcontains from 6 to 8 percent mineral filler. The paper sized with rosinand alum and weighs about 52 pounds per ream (500 sheets 25" X 38"). Oneside of the paper is base-coated with l pounds per ream dry weight of acoating comprised of clay (I00 parts), casein (20 parts) and dimethylolurea (2 parts) and is then dried and calendered. The paper plate is thenreverse-roll coated with 2 pounds dry weight per ream of a xylenedispersion of a diorganopolysiloxane composition comprised of adimethylpolysiloxane, methylhydrogensiloxane and zinc octoate, and theresulting layer of diorganopolysiloxane is dried and cured for 40seconds at 500 F. The silicone rubber coated plate is then fed through aXerox 914 copy machine. As a result of this procedure, a powder imagepreviously electrostatically formed on a selenium-plated drum istransferred to the plate. This image is then heated to cause the powderparticles to fuse to each other and to the surface of the plate. Theplate thus prepared is then mounted on a rotary otfset duplicatorAddressograph Multigraph Corporation, Multilith No. [250) from which themolleton rollers (water fountain rollers) have been removed. The plateis merely clamped to the plate cylinder and while dry is inked withregular lithographic ink (Addressograph-Multigraph ink No. ML 36) by theinking roller and the image is printed on the offset blanket from whichit was transferred to a paper sheet. Fifty copies having clean un-inkedbackground areas are produced from this plate.

EXAMPLE 2 A paper substrate as prepared in Example 1 is air knife coatedwith 3 pounds per ream dry weight of a diorganopolysiloxane compositioncomposed of dimethylpolysiloxane having silicon-bonded hydroxy groups,methylhydrogen polysiloxanes and dibutyl tin laurate. Thediorganopolysiloxane composition is dispersed in toluene in an amountsufficient to provide a dispersion having about 10 percent by weight ofsolids. The coating layer is cured at 300 F for about 5 minutes. Thisplate is then sensitized by rubbing the silicone rubber surface with acotton pledget filled with powdered double chloride of zinc and thepara-formaldehyde condensate of diazotized para-aminodiphenyl amine.Excess diazo powder is then carefully wiped off. The sensitized platethus prepared is then exposed through a negative transparency to a 35amp. double carbon are at a distance of 36 inches for one minute. Thepartially exposed plate is then washed or developed with water to removethe diazo compound from the unexposed areas. The plate thus prepared wascompletely dried and clamped to the plate cylinder of a rotary ofisetduplicator as described in Example I and the plate inked and employed toproduce over 50 copies. The copies thus produced were clean with notoning or inking in the background areas.

EXAMPLE 3 An aluminum based diazo sensitized plate is prepared bycoating an aluminum plate with an aqueous solution of sodium silicateand thereafter coating the silicated surface with an aqueous 1 percentsolution of the double salt of zinc and condensate of para-formaldehydeand para-diazo-diphenyl amine as described in U.S. Pat. No. 2,714,066.After the diazo coating has dried, a layer of the diorganopolysiloxanecomposition is applied by Mayer bar coater. The diorganopolysiloxanecomposition comprises dimethylpolysiloxane gums, silane oxime andtitanium dioxide. The surface bearing the diorganopolysiloxane coatingis wiped down with a soft cloth to leave a film which has a thickness of0.05 mils after curing for about 12 hours at room temperature. The platethus prepared is exposed through a positive transparency for 60 secondsto a 35 ampere double are at a distance of 36 inches. Following theexposure, the surface of the exposed plate is swabbed with a watersolution containing a small amount of Eastman Kodak's FOTOFLO, a wettingagent. This water removes the silicone layer and soluble diazo compoundfrom the unexposed areas, laying bare the surface of the originalsubstrate in these areas. Thereafter, the plate is dried, mounted on arotary press as described in Example 1, inked and employed to producel,000 clean copies.

EXAMPLE 4 A 5 mil sheet of aluminum foil having a surface roughened bysand blasting is coated with a 0.2 mil layer of a diorganopolysiloxanecomprised of hydroxyl end-blocked dimethylpolysiloxane andvinyltriacetoxy silane, said composition on curing forming an acetoxyend-block vinyl substituted dimethylpolysiloxane silicone rubber.immediately thereafter while the diorganopolysiloxane layer is stillliquid, a 3 mil sheet of soft copper foil is pressed into intimatecontact with the aforesaid layer. The sandwich so formed is allowed toage for 72 hours. Following the aging period, the exposed surface of thecopper is cleaned by immersing for two minutes in a standard etchingsolution consisting of the following:

milliliters of calcium chloride solution of 40-4l F Baume,

380 grams of zinc chloride,

285 milliliters of ferric chloride solution of 50-5 l F Baume, and

I4 milliliters of 38 percent hydrochloric acid. Following the etchingprocedure, the copper surface is immediately washed and dried. The drycopper surface is then given a photo-resist layer of aphotopolymerizable material containing polyvinyl einnamate polymers. Thephoto-resist layer is dried and the surface exposed through a negativetransparency to the light from a 35 ampere double are at a distance of36 inches for 3 minutes. Following the exposure period, the surface ofthe plate is swabbed with developer which removes all of the unexposedphotopolymerizable material and leaves the underlying copper bare butdoes not remove the photopolymerized layer in the image area. Thesurface of the plate is then immersed in the same etching solution inwhich the copper was previously cleaned and allowed to remain thereuntil all the copper except that covered by the photopolymer image hasbeen dissolved. The plate is then washed and dried. The plate thusprepared is then mounted on a rotary press as described in Example Icoated with ink and used to print 10,000 copies.

EXAMPLE 5 A sand blasted aluminum plate is treated with sodium silicate,washed and dried, and thereafter sensitized by swabbing with an aqueous2 percent solution of a zinc salt of the condensate of para-formaldehydeand para-diazodiphenyl amine. Following the coating procedure the plateis dried and the dried plate exposed through a negative transparency for60 seconds to a 35 ampere double arc at a distance of 36 inches. Theimage so formed is developed by swabbing the surface of the plate withan emulsified colored nitrocellulose lacquer in an aqueous solution ofgum arabic. This procedure removes the diazo compound from the unexposedor background area but does not remove the exposed image. In addition,the emulsion breaks sufficiently to permit the lacquer to adhere to andcoat the surface of the image. The plate is then washed with water toremove all traces of the gum arabic from the surface of the platewithout removing the lacquer from the image area. Following the removalof the gum arabic, the plate is again swabbed all over with an aqueoussolution of the formaldehyde condensate of a para-diazodiphenyl aminesalt and then allowed to dry. The dried plate is then roller coated witha diorganopolysiloxane composition comprised of an acetoxy end-blockeddimethylpolysiloxane and dibutyl tin diacetate in an amount sufficientto provide about 35 grams per square meter of the diorganopolysiloxanecomposition. This layer is allowed to air-cure for 30 minutes and thenit is exposed over its entire surface to radiation from a 35 amperedouble arc lamp at a distance of 24 inches for 3 minutes. By thistreatment the diazo compound is insolubilized and its adherence to thesilicone layer improved, and likewise the silicone layer itself isfurther cured. Next, the plate is rubbed with a mixture of equal partsof l,l,l-trichloroethane and xylene and onefourth part of ethyleneglycol. This liquid penetrates through the silicone layer and loosensthe lacquer layer covering the image and the rubbing removes theloosened silicone rubber leaving the image area slightly recessed. Thedepressions thus formed are filled with polyvinyl acetate emulsion andallowed to dry. The resulting plate has a level surface, with imageareas of oleophilic polyvinyl acetate and ink repellent background areasof silicone rubber. The plate thus prepared is mounted on a lithographicpress as described in Example 1 and used to print 1,500 copies.

The various diorganopolysiloxane compositions employed in the presentinvention are known in the art and are prepared in accordance with knownmethods. Representative acetoxy end-blocked diorganopolysiloxanes to beemployed in the present invention, such as the dimethylpolysiloxanes,vinyl substituted dimethylpolysiloxanes, alkyl substituteddimethylpolysiloxanes, cyanoalkyl substituted dimethlypolysiloxanes and3,3,3-trifluoropropyl and other haloalkyl substituteddimethylpolysiloxanes, are prepared in accordance with methods known tothe skilled in the art as illustrated by the teachings of U.S. Pat. Nos.3,035,0l6 and 3,077,465. Representative diorganopolysiloxanecompositions comprised of dimethylpolysiloxanes having terminalsilicon-bonded hydroxy groups, methyl hydrogen polysiloxane and dibutyltin dilaurate or dibutyl tin diacetate are also well known in the artand are produced in accordance with known methods. A representativemethod of production is taught in U.S. Pat. No. 2,985,545. Similarly,the diorganopolysiloxane compositions comprised of diorganopolysiloxaneshaving terminal siliconbonded hydroxy groups, an alkyl silicate and ametallic salt of an organic carboxylic acid are known in the art and areproduced by known methods such as the procedures taught by U.S. Pat. No.2,843,555.

The photo-responsive diazo compounds to be employed in the presentinvention are well known in the art. Representative diazo compounds aredescribed in U.S. Pat. Nos. 2,7l4,066 and 2,778,735, and include4-N-benzyl-N-ethyl)- amino-aniline,4-(N-2,6-dichloro-benzyl)-aminoaniline, 4- (N-cyclohexyl)-amino-aniline, 4-amino-2,5 ,4'-tribromodiphenylamine, 4-amino-2', 4',6'-trichloro-diphenylamine, 4- amino-Z-I N-( 2,5-diethoxy-phenyl)-sulfamido l-diphenylamine,4amino-3,6-dimethoxy-diphenylamine-Z'-carboxylic acid,l-amino-2,5-di-n-propoxy-4'-methyl-diphenylsulfide, N-(2,6-dichlorobenzyl )-3-amino-carbazol, 4-( N-2,3,4,6-tetrachlorobenzyl)-amino-aniline, 4-(N-2,6-dichloro-benzyl-N-ethyl)-amino-2,5-diethoxy-aniline and 4-amino-2,5,4'-triethoxy-diphenylether and their aldehyde condensates and thesulfonates of both.

The term conventional lithographic ink as employed in the presentinvention refers to the inks commonly employed by those skilled in theart and may be generally defined as being highly pigmented varnished ofheat-bodied linseed oil or the equivalent and giving inkometer valuesfrom about l2-20 when measured at 90 F and 400 r.p.m. The inkometervalues are standard test values and the test is fully set forth in U.S.Pat. No. 2,101,322.

lclaim:

l. A dry planographic printing plate comprising a base layersufficiently strong to withstand the stresses normally encountered in aprinting process, and at least two additional layers disposed insuperimposed relation to each other and both overlying said base layer,one of said additional layers being a layer of silicone rubber materialand another of said additional layers being capable of being removed inselected areas so as to definetheboundaries of an image to be printedfrom said plate, said silicone rubber material being adapted in theabsence of dampening to provide an ink repellent background for saidimage.

2. A dry printing plate comprising a base layer having sufficientstrength to withstand the stresses normally produced by a printingprocess, a layer of silicone rubber material overlying said base layer,and a continuous chemically etchable metallic layer mounted on theoutside surface of the silicone rubber layer and capable of being etchedaway in selected areas so as to define the boundaries of an image to beprinted from said plate, said silicone rubber material being adapted inthe absence of dampening to provide an ink repellent background for saidimage.

3. The printing plate of claim I wherein said second layer overlies saidlayer of silicone rubber material.

4. The printing plate of claim 1 wherein said second layer is betweensaid layer of silicone rubber material and said base layer.

5. A dry planographic printing plate comprising a base layer and atleast two additional layers disposed in superimposed relation to eachother and both overlying said base layer, one of said additional layersbeing a layer of silicone rubber material, and another of saidadditional layers being light sensitive and capable of being removed inselected areas so as to define the boundaries of an image to be printedfrom said plate, said silicone rubber material being adapted in theabsence of dampening to provide an ink repellent background for saidimage.

6. The printing plate of claim 5 wherein said light sensitive layeroverlies said layer of silicone rubber material.

7. The printing plate of claim 5 wherein said light sensitive layer isbetween said layer of silicone rubber material and said base layer.

8. An imaged dry planographic printing plate, which accepts ink in theimage area and prints therefrom, and repels ink in the non-image area,comprising a base layer, an inkreceptive image area, and a siliconerubber material overlying said base layer and providing the inkrepellent non-image area.

9. A process for printing planographically in the absence of dampeningwith an imaged dry planographic printing plate which accepts ink in theimage area and prints therefrom and which repels ink in the non-imagearea, which process comprises rolling the surface of the imaged dryplanographic printing plate with ink in the absence of dampening wherebythe ink is contacted with the image and the non-image areas of theplate, the ink being repelled in the non-image area by a silicone rubbermaterial and the ink being accepted in the image area, and thereaftertransferring ink accepted in the image area to an ink-receptive surface.

i I i l i

2. A dry printing plate comprising a base layer having sufficientstrength to withstand the stresses normally produced by a printingprocess, a layer of silicone rubber material overlying said base layer,and a continuous chemically etchable metallic layer mounted on theoutside surface of the silicone rubber layer and capable of being etchedaway in selected areas so as to define the boundaries of an image to beprinted from said plate, said silicone rubber material being adapted inthe absence of dampening to provide an ink repellent background for saidimage.
 3. The printing plate of claim 1 wherein said second layeroverlies said layer of silicone rubber material.
 4. The printing plateof claim 1 wherein said second layer is between said layer of siliconerubber material and said base layer.
 5. A dry planographic printingplate comprising a base layer and at least two additional layersdisposed in superimposed relation to each other and both overlying saidbase layer, one of said additional layers being a layer of siliconerubber material, and another of said additional layers being lightsensitive and capable of being removed in selected areas so as to definethe boundaries of an image to be printed from said plate, said siliconerubber material being adapted in the absence of dampening to provide anink repellent background for said image.
 6. The printing plate of claim5 wherein said light sensitive layer overlies said layer of siliconerubber material.
 7. The printing plate of claim 5 wherein said lightsensitive layer is between said layer of silicone rubber material andsaid base layer.
 8. An imaged dry planographic printing plate, whichaccepts ink in the image area and prints therefrom, and repels ink inthe non-image area, comprising a base layer, an ink-receptive imagearea, and a silicone rubber material overlying said base layer andproviding the ink repellent non-image area.
 9. A process for printingplanographically in the absence of dampening with an imaged dryplanographic printing plate which accepts ink in the image area andprints therefrom and which repels ink in the non-image area, whichprocess comprises rolling the surface of the imaged dry planographicprinting plate with ink in the absence of dampening whereby the ink iscontacted with the image and the non-image areas of the plate, the inkbeing repelled in the non-image area by a silicone rubber material andthe ink being accepted in the image area, and thereafter transferringink accepted in the image area to an ink-receptive surface.